1. Field of the Invention
The present invention relates to a laser diode device having a photodetector which detects laser light, more specifically to a laser diode device which can be suitably used for optical disks.
2. Description of the Related Art
A laser diode device for optical disks in a related art includes a photodetector which detects laser light from a laser diode included in the laser diode device. Typically, the photodetector is arranged in a region where the output of light from the laser does not decay, for example, on a rear end surface side of the laser diode (a side opposite to a light emission side) separate from the laser diode, and the photodetector detects laser light by absorbing light leaked through the rear end surface to convert the light into a current signal.
However, in general, the rear end surface of the laser diode is covered with a high-reflectivity film, so the output of light leaked through the rear end surface is extremely small. Therefore, it is necessary for the photodetector to have a high sensitivity to the leaked light. At present, as the laser diode for optical disks, a multiwavelength laser capable of outputting laser light of 780 nm wavelength used for replaying a CD (Compact Disk) or recording on or replaying a recordable optical disk, such as a CD-RW (CD Rewritable) or an MD (Mini Disk), or laser light of 650 nm wavelength used for recording on or replaying a DVD (Digital Versatile Disk) is the mainstream. Therefore, for example, as described in Japanese Unexamined Patent Application Publication No. 2004-55744, a photodiode (PD) made of a silicon (Si)-based compound semiconductor which can obtain high sensitivity to such long-wavelength light is used as a photodetector.